The present invention relates to a fan motor used in a dehumidifier, an insecticidal apparatus or the like for realizing low current, low noise and long life.
In a related art, an electric fan used in a dehumidifier or the like is proposed (refer to, for example, Patent References 1 through 3, 8). The related arts do not take driving an electric motor by a battery into consideration and are not to realize low current, low noise and long life.
In contrast thereto, there have been proposed a technology (refer to, for example, Patent Reference 4) with regard to a control for restraining current consumption by detecting an effect by a fan motor and controlling (reducing) a revolution number of the fan motor, or intermittently driving the fan motor in accordance with an amount of the effect to achieve low power consumption of the fan motor, a technology (refer to, for example, Patent reference 5) constituted by a single blade using a piezoelectric element and the like.
However, when constituted by the single blade, a booster circuit is required and therefore, the fan motor becomes expensive.
Further, there is known a single phase stepping motor for a timepiece as a low current consumption type motor (refer to, for example, Patent References 6, 9), however, a torque thereof is very small and therefore, such a motor is difficult to be applied to a fan motor.
Although there is proposed a fan motor constituting a drive source by a stepping motor in Patent Reference 7, the motor cannot be started and becomes out of phase by driving the motor by a low current since a moment of inertia of an impeller is large and it is hard to realize low current driving.
Further, the Patent References 2, 3 disclose a constitution in which a motor shaft is provided with a fan receiving portion, and a fan is driven by a friction between the motor shaft and the fan receiving portion, however, the constitution is for stopping the fan even when the motor is rotating in the case that the apparatus is inclined, a clearance is provided in a radial direction between the motor shaft and the fan and therefore, there is a case of shifting a gravitational center of the fan of the motor shaft to thereby cause a deterioration in balance, vibration, or noise.
Patent Reference 1: JP-UM-A-2-100631
Patent Reference 2: JP-A-3-154613
Patent Reference 3: JP-A-11-197438
Patent Reference 4: JP-A-U-5622
Patent Reference 5: JP-T-2000-513070
Patent Reference 6: JP-B-61-11390
Patent Reference 7: JP-A-10-36634
Patent Reference 8: JP-A-5-153892
Patent Reference 9: JP-A-8-255859
In view of the above-described situation, in the related art, a DC motor with a blush increasing a resistance value of a rotor is used as a fan motor to provide a no load current of several mA, however, since the motor is driven continuously for a long period of time, wear of the blush is brought about and life there of poses a problem. Therefore, it is conceivable to use a blushless motor which is not provided with a contact of a blush or the like to prolong life thereof, however, in the case of the blushless motor, at least several mA of current is needed only for a hall element, several tens mA of current consumption is needed including energization of other driving circuit or the motor, and therefore it is difficult to drive the motor continuously for a long period of time by using, for example, a battery.
Further, it is conceivable to use a sensorless motor which is not provided with a hall element, however, since a reversing current of a coil is detected a starting characteristic needs to be high, as a result, low power consumption formation is difficult and the motor becomes expensive. Further, it is possible to realize a low current driving by using a stepping motor which does not need a hall element is used. However, since a starting torque is small, when an object having a large moment of inertia such as an impeller is intended to drive to rotate, the stepping motor can not be started but becomes out of phase and therefore it is difficult to drive the stepping motor by a low current.